JP2005519729A - Chemical processing by non-thermal discharge plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To activate a chemical reaction using a non-thermal capillary discharge plasma (NT-CDP) unit or a non-thermal slot discharge plasma (NT-SDP) unit (collectively referred to as “NT-CDP / SDP”). Method.
An NT-CDP / SDP unit includes a first electrode provided between two dielectric layers (8, 9), and the first electrode and the dielectric layer have at least one through hole (for example, a capillary). And slots). A dielectric sleeve (3) is inserted into the through hole, and at least one second electrode (2) (for example, a pin, ring, metal wire, tapered metal blade, etc.) is combined. And provided in fluid communication with the through-hole. When a voltage difference is applied between the first electrode and the second electrode, a non-thermal plasma discharge is radiated from the through hole. Then, the chemical raw material to be processed is exposed to non-thermal plasma. This processing involves the following exemplary chemical reactions: (i) partial oxidation of hydrocarbon feedstock to produce organic compounds with functional groups introduced; (ii) polymer fibers (eg, PAN fibers in carbon fiber production) Chemical stabilization of precursors), (iii) pre-reforming of long-chain petroleum hydrocarbons to produce feedstock suitable for reforming, and (iv) chemical reduction to produce carbon monoxide and hydrogen gas. It is suitable for reforming natural gas in an atmosphere (for example, ammonia or urea) and (v) plasma enhanced water gas conversion.

Description

Related Application Indication This application is a continuation-in-part of US patent application Ser. No. 09/738923 filed on Dec. 15, 2000. Further, this application claims the benefit of US Provisional Application No. 60/309530 filed on August 2, 2001 and 60/358340 filed on February 19, 2002, and The entire description of the application is incorporated herein as part of this specification.

TECHNICAL FIELD OF THE INVENTION The present invention relates to chemical processing utilizing plasma. In particular, the activation of specific chemical species is performed more uniformly than when using conventional discharge techniques (for example, arc, gliding arc, dielectric barrier discharge (DBD), corona), so that high yield and Use of non-thermal capillary discharge plasma (NT-CDP) and non-thermal slot discharge plasma (NT-SDP) (collectively referred to as “NT-CDP / SDP”) to achieve high energy efficient chemical conversion About. Unlike conventional discharge techniques, which tend to create a spatially and temporally inhomogeneous filamentary discharge, NT-CDP / SDP devices minimize spatial inefficiencies. A stable plasma is generated over a wide range while retaining the same, and the same processing as the conventional one can be performed reliably. Moreover, since the NT-CDP / SDP apparatus can be specifically adjusted so as to selectively start a specific rate-limiting chemical reaction, the reaction can be easily advanced in a direction to obtain a desired product. . By energizing the system in such a specific way, chemical reactions that are normally possible only at high temperatures and pressures can occur under atmospheric conditions. Adjustments are made by changing power, reactant composition and concentration, carrier gas composition and flow rate, temperature, pressure, and / or reactor geometry.

  The use of electrical discharges to initiate industrially important chemical reactions is already known and has been used for a long time. An example of the oldest and most efficient chemical transformation that occurs in the presence of an electrical discharge is the production of ozone. The generated ozone can be reacted with unsaturated hydrocarbons, thereby synthesizing ozonated products, aldehydes, and ketones. Early typical gas discharge devices operated on the basis of exposure of various reactive gases to an electric arc (thermal plasma) (Knight, by Henry de Boyne, “ Arc discharge; its application to power control, London, Chapman & Hall, (1960)).

  Recent innovations have led to the use of both thermal and non-thermal plasmas in chemical processing. U.S. Pat. No. 6,372,192 issued to Paulauskas et al. Describes a method for producing carbon fibers using plasma. In the method of this patent, stabilized polyacrylonitrile (PAN) fibers (first step in carbon fiber processing) are converted to carbon graphite fibers by a plasma at a GHz frequency in a low pressure oxygen-free atmosphere. However, this patent does not disclose or suggest the use of an oxygen rich plasma to stabilize PAN fibers in the early stages of the process. Can this patent teach the use of non-thermal plasmas?

  In recent years, research and development in the fields of fuel reforming and fuel conversion using plasma have also made great progress. This is mainly due to the renewed interest in hydrogen fuel cells. For example, U.S. Pat. No. 6,322,757 issued to Cohn et al. And references cited therein provide a plasma fuel converter (such as a plasmatron) for reforming hydrocarbons to produce hydrogen-rich gas. Disclosure. US Pat. No. 6,395,197 issued to Detering et al. Describes the conversion of light hydrocarbons (natural gas) into the desired end product, in particular diatomic hydrogen and elemental carbon, at high temperatures. The device and method of operation are described. In another patented invention (US Pat. No. 6,375,832 granted to Eliasson et al.), A gas containing a large amount of hydrogen (such as methane) and carbon (such as carbon dioxide) is chemically converted into a liquid fuel in a normal state. A method of conversion is taught. Fischer Trop synthesis using this plasma is performed using a dielectric barrier discharge in combination with a solid zeolite catalyst.

  Another area of great interest in plasma processing includes areas of plasma activated surface treatment that increase the wettability and / or surface adhesion of polymeric materials. For example, LA Rosenthal and DA Davis, “Electrical Characterization of a Corona Discharge for Surface Treatment”, IEEE Transaction on Industry Applications (IEEE processing in industrial applications), 1A-11, No. 3, pages 328-335 (May / June 1975); Han, S. Han. Lee, Y. Lee Kim, H. Kim G. Kim, J.H. J. Lee, J. Lee J. Yoon, G. G. Kim's paper "Polymer Surface Modification by Plasma Source Ion Implantation", Surfaces & Coatings Technology, Vol. 93, pages 261-264. (1997) and US Pat. No. 6,399,159 to Grace et al.

  Therefore, it is desirable to optimize chemical processing by using NT-CDP / SDP. This is described in US patent application Ser. No. 09 / 728,923 filed on Dec. 15, 2000 and No. 60/358340 filed on Feb. 19, 2002, all of which are incorporated herein by reference. Is incorporated herein by reference as a part thereof.

  The present invention relates to a method for improving chemical processing. Specifically, the present invention relates to a method for activating chemical reactions using NT-CDP / SDP units. The NT-CDP / SDP unit in the present invention includes a first electrode provided between two dielectric layers, and the first electrode and the dielectric layer have at least one through hole (for example, a capillary or a slot). At least one second electrode (eg, in the form of a pin, ring, metal wire, tapered metal blade, etc.) is provided in fluid communication with the combined through-hole. When a voltage difference is applied between the first electrode and the second electrode, a non-thermal plasma discharge is radiated from the through hole. Then, the chemical raw material to be processed is exposed to non-thermal plasma. This processing is suitable for the following exemplary chemical reactions. (I) partial oxidation of hydrocarbon raw materials to produce organic compounds with functional groups introduced; (ii) chemical stabilization of polymer fibers (eg, PAN fiber precursors in carbon fiber production); (iii) Pre-reforming of long-chain petroleum hydrocarbons to produce feedstock suitable for reforming, (iv) natural in a chemical reducing atmosphere (eg ammonia or urea) to produce carbon monoxide and hydrogen gas Suitable for gas reforming and (v) plasma enhanced water gas conversion.

  The foregoing and other features of the present invention will become more readily apparent from the following detailed description of exemplary embodiments of the invention and the drawings. Here, in similar drawings, similar symbols represent similar elements.

  The present invention relates to a method of activating (catalyzing) a chemical reaction. Exposure of the chemical source to a discharge provided within the plasma volume can improve the yield and / or energy efficiency of certain chemical transformations. Processing of gaseous, liquid, aqueous and / or solid precursors is possible. The following are some examples of exemplary chemical reaction types that are enhanced upon exposure to NT-CDP / SDP, along with specific exemplary reactions.

(I) Partial oxidation of a hydrocarbon raw material to produce an organic compound into which a functional group has been introduced, such as alcohol, aldehyde, ketone, carboxylic acid.
Example

(Ii) Chemical stabilization “oxidation” of the PAN precursor in the carbon fiber production pathway.
Example

(Iii) Pre-reforming ("cracking") of long chain petroleum hydrocarbons to produce feedstock suitable for reforming.
Example

(Iv) Natural gas reforming in a chemically reducing atmosphere (ammonia or urea) to produce carbon monoxide and hydrogen gas.
Example

(V) Plasma enhanced water gas conversion reaction.
Example

In the processes (i) and (ii), non-thermal partial oxidation of hydrocarbon feedstock (“low temperature combustion”) is activated by NT-CDP / NT-SDP. By plasma, the following oxidizing species from the ambient air, i.e. oxygen atom (O ⁽¹ D)), hydroxyl radical (OH), ozone (O _3), and peroxide radical (HO ₂₎ is generated, the gas stream Sent in. These highly reactive species then selectively oxidize hydrocarbon molecules and the reaction produces the desired product. In the case of example (i), the target product is CH ₃ (CH ₂ ) _n CH ₂ OH.

  The reaction (iii) is preferably carried out in a chemically neutral plasma. The term “chemically neutral” means an environment having a chemically inert carrier gas (including but not limited to helium), which is due to direct electron impact. Obtained by dissociation. Processes iv) and v) described above occur preferentially in a chemically reducing plasma. Chemically reducing plasma is plasma that tends to increase the number of electrons in the target chemical substance. (Reduction is the reverse of oxidation.) Addition of ammonia or urea to the gas stream facilitates the chemical reduction of hydrogen in methane (process (i)) or water (process (ii)) to hydrogen gas. It is possible to create an electron-rich plasma suitable for the generation.

  FIGS. 1 a-1 c show views from various directions of an exemplary cyclic NT-CDP processing unit that is particularly well suited for chemical stabilization (oxidation) of polymer fibers such as PAN fibers. This processing unit includes a second electrode 2, which is arranged between two insulating dielectric layers 8, 9 forming a hollow tube. The second electrode 2 is selected to have a desired expansion coefficient. Although the processing unit is shown and described as being cylindrical, other geometric shapes are also contemplated and are within the scope of the present invention. A high voltage bus 5 (for example, a wire mesh or an outer metal sheath) is provided around the outer dielectric layer 9.

  FIG. 1b is a cross-sectional view perpendicular to the longitudinal axis of the processing unit of FIG. 1a. As can be seen from FIG. 1b, a plurality of capillaries 4 are preferably provided radially outwardly through the dielectric layer 8, the second electrode 2 and the counter dielectric layer 9. A dielectric sleeve 3 made of quartz or the like is inserted into each capillary 4. A pin electrode 1 is embedded in each dielectric sleeve 3, and the pin electrode 1 is insulated from the second electrode 2. The high voltage bus 5 connects the row of pin electrodes 1 to a common high voltage source (HV). In an alternative configuration, as long as the electrode is in fluid communication with the capillary, the electrode may be of another geometric shape and need not necessarily be embedded in the capillary. Several alternative configurations of capillary discharge arrays are shown and described in US patent application Ser. No. 09/748923. FIG. 1c is an enlarged view of one of the capillaries shown in FIG. 1b.

  In operation, the PAN fiber 6 is inserted into this tubular passage and subjected to NT-CDP production. The PAN fiber 6 is subjected to NT-CD plasma discharge in the processing unit 10, and the stabilized PAN fiber 7 appears from the opposite end.

  2a and 2b are views of the NT-CDP gas phase chemical processing unit according to the present invention as seen from two directions. According to the cross-sectional view of FIG. 2 a, a set of capillaries 20 are provided through the dielectric sheet 11. A dielectric sleeve 12 is inserted into each capillary 20 to form a high dielectric current limiting capillary. Each capillary 20 has a pin-like or needle-like electrode 10 embedded therein. The row of pin-like or needle-like electrodes 10 is electrically connected to a common high-voltage source by a high-voltage bus 13 such as a wire mesh or a metal sheath. A dielectric plate 14 made of quartz, glass, ceramic or the like is used to insulate the electrode plate 15. The inlet transition 16 and the outlet transition 17 allow the gas to be processed to pass substantially across a row of capillary plasma jets having a reactor volume 21. The sealed manifold 18 is adapted to be ejected into the process stream after the gaseous chemical reagent has passed directly through the needle jet 10 and capillary 20 and into the plasma jet. Element 19 is an auxiliary reagent gas intake. In a preferred embodiment, the system is one that can be easily scaled in the range of about 500 watts to about 10 KW with respect to plasma power. The processing unit is preferably optimized to use a high frequency power source. The peak-to-peak voltage required between the reactor gaps is preferably in the range of about 5 KV to about 50 KV, depending on the carrier gas.

3a and 3b are graphs showing the results of an experiment for generating hydrogen by using NT-CDP from isooctane and ammonia vapor in a nitrogen carrier gas. To ensure a steady state reduction, the discharge was started after equilibration for 300 seconds. Specifically, FIG. 3a is a graph of the hydrogen detector reading (mA) in the H ₂ production experiment from NH ₃ versus time. The experiment was performed at a power of 200 W, an NH ₄ OH concentration of 15 M, and an N ₂ flow rate of 11 L / min. Figure 3b shows a graph of the ppm concentration of the H ₂ gas with respect to time. The experiment was performed at a power of 2000 W, an NH _{3 (aq)} OH concentration of 15 M, and an N ₂ flow rate of 11 L / min.

From these experimental results, when the NT-CDP configuration according to the present invention is used, there is almost no interference due to the plasma alone (N ₂ plot), and the modification of isooctane in a chemically neutral plasma is almost impossible. It was confirmed that only a small amount of hydrogen was produced in the quality (isooctane plot). The ammonia plot shows that a large amount (˜1000 ppmV) of hydrogen was generated by the disproportionation reaction due to the autocatalysis of ammonia. When isooctane was used in the presence of ammonia, the maximum amount of hydrogen (˜1500 ppmV) was produced due to its synergistic effect. GC / MS analysis performed on the product stream also shows that a large amount of plasma pre-reformation (cracking) has been performed in connection with this hydrogen production. Optimizing these results could provide an economically effective way to produce hydrogen gas from condensed fuel.

  The NT-CDP chemical processing method according to the present invention is advantageous in that it consumes very little power and minimizes wear over time of the catalyst compared to conventional thermal and / or catalytic methods. Low power consumption can be achieved because it is not necessary to heat a large amount of gas to cause the conversion. In addition, NT-CDP chemical processing is also advantageous compared to other plasma processes such as dielectric barrier discharge (DBD) and corona discharge (CD). This is because the use of NT-CDP makes it possible to realize a plasma that spreads in a relatively large volume, so that substantially homogeneous and efficient chemical processing can be obtained. The disclosed chemical processes are used for illustration and are not meant to limit the scope of the present invention as inapplicable to other chemical processing.

  4a-4c show an exemplary embodiment of an NT-SDP gas phase chemical processing unit according to the present invention. This embodiment is similar to the embodiment shown and described with respect to FIGS. 2a-2c, except that the unit uses a slot discharge configuration instead of a capillary discharge arrangement. The slot discharge configuration of FIGS. 4a-4c is particularly well suited for chemical stabilization of polymer fibers such as PAN fibers. The same reference numerals as described with respect to the units shown in FIGS. 2a to 2c represent the same reference elements. In FIG. 4a, the slots 4 are arranged substantially parallel to the longitudinal axis. Alternatively, the slot 4 may be provided in a spiral direction or may be provided substantially perpendicular to the major axis of the reactor. An electrode 4 is inserted in each slot. As an example, the electrode 4 can be a metal wire, in which case it is arranged to complement the shape of the corresponding slot and is partially inserted, embedded or provided in the vicinity of the slot. . In other embodiments, the slot may be a tapered blade. An alternative slot discharge configuration is described in US patent application Ser. No. 60 / 358,340, the entire description of which is hereby incorporated by reference. This slot discharge arrangement emits a plasma with a large surface area compared to the capillary discharge configuration.

  Thus, while the novel basic features of the present invention have been illustrated, described, and pointed out in the context of a preferred embodiment, those skilled in the art will recognize that the illustrated apparatus is within the spirit and scope of the present invention. It will be understood that various omissions, substitutions and changes may be made in the shape and details and operation thereof. For example, all combinations of elements and / or steps that perform substantially the same function in substantially the same way to achieve the same result are specifically intended to be within the scope of the present invention. All replacements of elements in one described embodiment with another embodiment are contemplated and contemplated. It should also be understood that the drawings are not necessarily drawn to scale, but are merely conceptual in nature. Accordingly, it is intended that the invention be limited only as indicated by the claims appended hereto.

  All documents, publications, and patents mentioned in this specification are hereby incorporated by reference in their entirety.

1 is a side perspective view of an exemplary cyclic NT-CDP processor according to the present invention for chemical stabilization (oxidation) of PAN fibers. FIG. 1b is a cross-sectional view perpendicular to the longitudinal axis of the device of FIG. FIG. 2 is an enlarged longitudinal sectional view of one capillary ring electrode in the apparatus of FIG. 1 is a cross-sectional view of an exemplary gas phase NT-CDP-based chemical processing unit according to the present invention. 2b is an enlarged view of one capillary of the apparatus of FIG. 2a. FIG. ₃ is an exemplary graph showing time versus hydrogen detector readings for H ₂ production from NH ₃ . 6 is an exemplary graph showing time versus hydrogen gas concentration. 1 is a side perspective view of an exemplary cyclic NT-SDP processor according to the present invention for chemical stabilization (oxidation) of PAN fibers. FIG. 4b is a cross-sectional view perpendicular to the longitudinal axis of the device of FIG. 4a. 4b is an enlarged longitudinal section of one longitudinal wire electrode in the apparatus of FIG. 4b.

Claims (16)

A method of activating a chemical reaction using a non-thermal discharge unit, the unit comprising a first electrode provided between two dielectric layers, wherein the first electrode and the dielectric layer are At least one through-hole, and at least one second electrode is provided in fluid communication with the combined through-hole, the method comprising:
Generating a nonthermal plasma discharge from the through hole by applying a voltage difference between the first electrode and the second electrode;
Exposing the chemical source to non-thermal plasma emitted from the through-hole. The method of claim 1, wherein the through hole is a capillary and the unit further comprises a dielectric sleeve inserted into the capillary. The method of claim 2, wherein the through hole is provided radially outwardly through the first electrode and the dielectric layer. The method of claim 2, wherein the second electrode is a metal pin or ring. The method of claim 1, wherein the through hole is a slot. 6. A method according to claim 5, wherein the through holes are arranged in a longitudinal direction, in a spiral direction or in a direction substantially perpendicular to the longitudinal axis. The method of claim 5, wherein the second electrode is a metal wire or a tapered metal blade. The method of claim 1, further comprising a voltage bus connecting the second electrode to a power source. The method of claim 8, wherein the voltage bus is one of a wire mesh or a metal sheath. The method according to claim 1, wherein the chemical reaction is partial oxidation of a hydrocarbon raw material to produce an organic compound having a functional group introduced therein. The method of claim 1, wherein the chemical reaction is chemical stabilization of a polymer fiber. The method of claim 11, wherein the polymer fiber is a polyacrylonitrile precursor used in carbon fiber production.   The process of claim 1 wherein the chemical reaction is a pre-reforming of long chain petroleum hydrocarbons to produce a feed suitable for reforming. The method of claim 1, wherein the chemical reaction is reforming of natural gas in a chemically reducing atmosphere to produce carbon monoxide and hydrogen gas. 15. A method according to claim 14, wherein the chemically reducing atmosphere is ammonia or urea. The method of claim 1, wherein the chemical reaction is plasma enhanced water gas conversion.

Images